# [lammps-users] Question on Bin size for Neighbor Searching (image attached)

Thank you for very quick reply, Paul. I mean if the cell size is 1/2 cutoff, then an atom in a central bin may neglect some neighbors in a bin far away.

For instance, atom i is in the middle of cell 0 may not check the atom j in cell 2 (because cell 2 is not adjacent to 0) even though the distance between them is smaller than cutoff (because the size of cell 1 is only 1/2 cutoff).

The skin parameter is only applied for atoms in the neighboring cells of cell 0 and then is not applicable to atom j in this case.
An illustration is attached for what I mean.

-Trung

Trung,

The neighboring cell and its neighbor are both included in the stencil describing the neighbors within the cutoff. Neighbors are not supposed to be included further away than the set cutoff. So, to use your example, say we have a cubic equi-length system, all cells are cubic too. The stencils include cells 1 and 2 away from the center cell, creating a sampling space of about 5 x 5 x 5 = 125 cells, give or take a few cells that are excluded because the fall outside of the cutoff. I think the total would be 117 if you adhere to this logic.

Pieter